This invention relates to the field of data acquisition and recording, specifically to data logging equipment that take readings of physical properties at predetermined intervals and store the readings in memory for later analysis.
Data logging equipment has undergone considerable improvement owing to advances in electronics. Where early units stored data in the form of a pen drawing on a paper chart or as analog signals on magnetic tape, units can now convert and store data in semiconductor memory in digital form. This form of storage allows easy input into computer systems for data analysis.
Many data logging systems are designed for a single specific task (such as aircraft flight data recorders) having only the interfaces, sensors, and memory required for that specific task. Other logging systems (such as those designed for general laboratory use) offer a greater number of configurations. Unfortunately, the flexibility of even the most general designs is limited by the number of available, input channels and by memory size constraints.
The typical data logging system consists of a central controller with memory, and a number of sensor interface channels. Even when these channels are configurable for different sensors the number of channels is limited. Should a user need just one additional channel a larger system with an upgraded central controller, more memory, and many more channels is required. This can often lead the user to purchase a larger system than needed to insure that it will be adequate for possible future requirements. In addition to the higher cost of more capable systems, their physical size limits their usefulness in many portable applications.
Some systems include a great deal of computational analysis powerxe2x80x94adding cost and complexity. Since general purpose computers are widely available, the need for such power within the logging system is questionable.
Clearly, there is a need for a data sensing and logging system with the flexibility to address a range of tasks, that can be adequately expanded, where only the features required for a particular application need be included, and where minimal size and complexity insure portability. The present invention fulfills all these needs.
The present invention is an apparatus and method for periodic acquisition of data through the use of sensors and/or electronic interfaces. This data is stored in electronic memory for future computer analysis. The apparatus is modular, having a control module and zero or more acquisition modules. The control module provides timing and control information to the acquisition modules. It also provides the interface functionality for communication to a host computer. Each acquisition module contains circuitry to make measurements of one or more physical property and convert the measurement into a digital value. Temperature, altitude, airspeed, engine speed, gravitational force, magnetic force, pulse width, voltage, and current are but a few examples of physical values that may be measured. Each acquisition module also contains electronic memory in which to store the digital value. Additionally, each acquisition module has an interface link to the control module.
Having each acquisition module measure and store a single physical property gives the greatest flexibility in choosing modules for a specific application. However, it may be economical and useful to combine more than one acquisition function into a single module, or even add acquisition module functionality to the control module.
A typical system would consist of a control module and several acquisition modules. The acquisition modules would be selected to measure those physical values of interest for a specific application. In operation the control module would keep track of elapsed time and periodically signal the acquisition modules to make readings and store values. The amount of time between readings would be previously programmed into the control module and would be application dependent. This mode of operation of making periodic measurements and storing values is the data logging mode. In the data logging mode the system need not be attached to a host computer. Often the system would be in a remote location while in the data loging mode.
When data logging is complete, the system is attached to a host computer through an interface on the control module. The data stored in each acquisition module is then transferred, via the control module, to the host computer. Software within the host computer can then store, analyze, chart, or otherwise process the data. Calibration values for correction of acquisition sensor gain, offset, linearity, or other factors may be stored in a separate parameter area within each acquisition module""s memory. These values can then be used by the host computer to adjust and correct the acquired data.
The host computer can also send commands to the modules to perform functions such as clearing the module memory and setting the period between data readings.